Feet serve as a base for supporting a human body, and each foot is known to comprise of 28 bones, 107 ligaments, 32 muscles, and 57 joints. It is the most complicated musculoskeletal system in the human body. Primary joints thereof comprise an ankle joint, a subtalar joint, a transverse tarsal joint, a metatarsophalangeal joint and an interphalangeal joint.
In general, feet can be classified into 3 different types according to the height of the plantar arch: pes cavus, normal foot and flat foot. During the walking of people with flat feet, normally, due to the fallen arch, there is a greater over pronation during the period from the heel strike to midstance of the feet such that it tends to cause an excessive supination upon the period of push-off of the feet. Consequently, the heel and the metatarsus of people with flat feet would have a higher plantar pressure level comparing to a standard level of people with normal foot. Under normal activities, no special symptom may occur; however, in a long-term period, the feet are likely to produce fatigue, pain or even plantar pathological changes in comparison to those of the people with normal foot, which may also lead to injuries to knee joints and vertebral column joints. For people with flat feet, due to the longer time in excessive pronation on the feet, they prone to cause foot joints, ankle joints and lower limbs to bear excessive strains and the compensatory over internal rotation of hip joints; further leading to excessive pressures and lateral pulling force in medial patella; leading to pain in patella, chronic foot strain, tendinitis, plantar fasciitis, and metatarsalgia.
To keep the balance of body and the stability of forward movements during walking, the relative motions produced by the foot and joints thereof are highly complicated. The foot adjusts motions of each foot joint with tendons, ligaments, and other soft tissues of the foot for the stability while walking and adjusts to different environments. When a human body walks or runs, relative motions between the foot and the ground can be classified into 3 stages: heel rocker, ankle rocker and forefoot rocker. When the foot touches the ground, the reaction force applies on the calcaneus and rapidly increases during the initial contact of heel strike. At this moment the reaction force will reach 40 percent of the weight in 0.05 second; reaching 110 percent to 120 percent of the weight in 0.13 second (loading response). Follow by the forward swinging of body, the center of pressure moves forward from the hindfoot. The reaction force of forefoot reaches over 120 percent of weight during the period of push-off of the foot, and such reaction force is even higher during running.
The lateral side midfoot may occasionally contact with the ground moderately, and the reaction force of this area is often only 10 percent of the body weight. The pressure of metatarsus varies accordingly with differences of each individual. Usually the highest pressure level appears between the 2nd and 3rd metatarsals. People with pes cavus have higher plantar pressure in the hallux and 1st metatarsal. People with low arch or flatfoot usually have higher plantar pressure in the 1st, 2nd, 3rd metatarsals and heel.
During the walking of people with pes cavus, due to the insufficient tibial internal rotation affecting under pronation, they tend to have an excessive supination during push-off, which further leads to stiff walking postures and causing muscular and skeletal problems with high arch. The ankle joint has bigger flexion motion during ankle rocker to compensate the over plantar flexion angle of metatarsus and to increase the clearance altitude of the point of foot during push off. In addition, high arch runners clearly bear more impact forces than low arch runners do.
Genu Valgum and Genu Varum: the foot is constructed by a femur, a tibia, a fibula and a patella. When doing an X-ray photography research, a normal angle between tibia and femur diaphysis is outward 6° when observing in the coronal plane; Genu Valgum (X-leg) or Genu Varum (O-leg) is called if the angle is too big or too small. An easy clinically observing way would be making an individual put both knees forward and both medial side ankles together; if the width of at least two fingers can be put in between both knees, wherein, calling Genu Varum will cause excessive tibia external rotation and excessive forefoot supination while walking. The abnormal use of lower limb muscles further leads to pain in medial side of knees and metatarsus or even osteoarthritis. If an individual can put the width of at least two fingers in between medial side of ankles when both knees are put together, thereof is called Genu Valgum. This type of lower limbs causes knees and ankles to roll inward while stepping forward; in a long term, malaise of lateral knee joints and plantar fasciitis may occur.
Customized foot orthoses can increase contact area, rearranging forces to reduce plantar pressure. In current years, foot orthoses are commonly used in amending and assisting walking for foot dysfunctions that are caused by poor foot structure or other problems in the musculoskeletal system. Since 1983, research studies have demonstrated that foot orthoses can reduce symptoms of lower limbs. Such devices may be able to reduce the pains caused by plantar fasciitis by 80%, in addition to that it is able to facilitate the healing of the feet of injured runners.
Another significant purpose of foot orthoses is to make biomechanical behaviors to become normal. Many researches show that foot orthoses can reduce pronation or motion speed on the hindfoot. The arch supportive insole affects lower limb motions obviously; during running, it is able to reduce the tibia internal rotation by 2° for an early period of 50% time of standing. Such influence on the tibia axial rotation and varus and valgus of calcaneal is able to lower internal and external rotation speeds and tibia internal rotation angles in order to further reduce the plantar pressure at the hallux and the medial side of heel by 30%˜40%.
Known arch supportive insoles mainly provide a compensation of a raised height beneath the navicular by using an insole to compensate the plantar arch heights of pes cavus or flat foot in order to allow the foot to absorb impact and to achieve the effect of distributing the human body weight. Although known arch support insoles are helpful to muscular soreness associated with flat foot or pes cavus, the method can only raise the navicular medial side of midfoot such that it is only helpful in improving relative movements of midfoot and forefoot. For patients of flat feet with valgus heel or having pes cavus with under pronation, the motions of the subtalar joint cannot be effectively improved. Said damage to the musculoskeletal system still remains to exist for those using such known arch supportive insoles for exercises in a long term.
In view of the drawbacks of the known technique, the inventor of the present invention provides a device for three-dimensional foot motion control and plantar pressure redistribution, and said device for three-dimensional foot motion control and plantar pressure redistribution can be used for supporting the plantar arch and calcaneus without occupying excessive interior space of shoes, adjusting excessive subtalar joint valgus and varus, modifying angles of ankle supination and pronation, reducing improper motions of lower limb muscles; thereby, improving muscular soreness during walking or running, and reducing damage to skeletons and muscles.